WinForms project templates use latest C# language idioms

[DamianEdwards]

In .NET 6, the included C# project templates will use the latest language idioms.

See the parent Epic for details.

@OliaG

[RussKie]

Related:

• Windows Forms VB project template should have implicit imports instead of explict #1678
• Update C# templates to top level statements #5071
• Update C# templates with global usings #5074
• Update implicit global usings feature #5409

[DamianEdwards]

@RussKie just making sure you're aware of the SDK feature being implemented to support implicit/default global usings. There's a PR going on right now to enable this and then the WindowsDesktop SDK should utilize this feature too.

[vlada-shubina]

Just a hint since this repo is also using --langVersion: in project common templates we discovered issues to due to new features are only working in certain frameworks / language versions, so we are considering to conditionally enable features based on language version set by user (if set).
Draft PR on this is here: dotnet/templating#3454.

[DamianEdwards]

The compiler with support for this is now in SDK version 6.0.100-preview.7.21364.4

[RussKie]

@vlada-shubina could you guide me through the changes we need to make in our templates? Do we need to copy the changes from dotnet/templating#3454?

[vlada-shubina]

@vlada-shubina Vlada Shubina FTE could you guide me through the changes we need to make in our templates? Do we need to copy the changes from dotnet/templating#3454?

Since the templates allow the user to pick up the language version (and also framework in your case) you need to consider it when making the change, as if the user picks up lower language version or lower framework the template based on latest C# features may fail on build.

Generally for each feature you introduce to your templates you need to do the following conditions:

#ifdef (<framework supports the feature> &&<language version supports the feature>)
<updated code for the feature>
#else
<old code>
#endif

In case of console/classlib it was quite straightforward, as the content is very simple; but it might be more complicated with more code in the template..

I would recommend the following approach:

• define regex match generator for each lang version conditions needed (see csharpNorLater symbol in my PR)
• define computed symbol for each feature in use (see csharpFeature_ImplicitUsings for example in my PR)
  • note in your case conditions might be different in case template supports more frameworks - for console template we only support net6.0 so conditions just rely on langVersion, for classlib we additionally support netstandard2.0 and netstandard2.1, so the conditions exclude not supported frameworks
• use conditions in your code to enable / disable features (see cs and csproj files in my PR).

You can follow the way we did for console/classlib but direct copy-paste won't work - you need to adapt it for your template content.

I would also recommend to run the tests on all possible combinations of templates/frameworks/language versions to see if the template can be instantiated and at least built successfully, and assert if file content is as expected.

[vlada-shubina]

Additional thought: if your template code file content is too difficult to manage with inline conditions, you may consider doing different files and pick up the correct file to use using sources based on condition.
You already use this approach in some templates to pick up correct csproj file:

winforms/pkg/Microsoft.Dotnet.WinForms.ProjectTemplates/content/WinFormsApplication-CSharp/.template.config/template.json

Lines 82 to 103 in e0c821b

	"sources": [
	{
	"exclude": [ "**/[Bb]in/**", "**/[Oo]bj/**", ".template.config/**/*", "**/*.filelist", "**/*.lock.json" ],
	"modifiers": [
	{
	"condition": "(UseWindowsDesktopSdk)",
	"exclude": [
	"Company.WinFormsApplication1.csproj"
	],
	"rename": {
	"Company.WinFormsApplication3x1.csproj": "Company.WinFormsApplication1.csproj"
	}
	},
	{
	"condition": "(!UseWindowsDesktopSdk)",
	"exclude": [
	"Company.WinFormsApplication3x1.csproj"
	]
	}
	]
	}
	],

---

Btw, I saw some templates following this approach with sources which is a bit easier impo (especially if conditions are exclusive):
folder structure

- .template.config 
- shared  - the files to be used always
- conditionA - the files to be used when conditionA is met
- conditionB - the files to be used when conditionB is met

then template.json looks like:

 "sources": [
    {
      "source": "./shared",
      "target": "./"
    },
    {
      "condition": "(conditionA)",
      "source": "./conditionA",
      "target": "./"
    },
    {
      "condition": "(conditionB)",
      "source": "./conditionB",
      "target": "./"
    },
  ],

This allows to avoid renames, excludes etc. However it's just a suggestion in case you want to use sources for new features, and it makes your life easier.

[RussKie]

@vlada-shubina thank you!

[RussKie]

Nullability was enabled in our templates by @jmarolf in #4922